Our flirtation with a full-blown NASCAR-style side-exit exhaust system has uncovered several interesting discoveries. When we first built our NASCAR system from Dr. Gas parts in the November 2009 issue (see "The 'X' Factor"), we gave the warning that you could run afoul of the local gendarmes if they didn't fancy your automotive style. Well, it turned out the cops didn't dig it so much. After two run-ins, we found ourselves either leaving the Laguna in the garage, or driving it like there was an egg under the gas pedal. Make no mistake about it, the Dr. Gas side-exit exhaust is bitchin. We like getting noticed (most of the time), and it was a great conversation starter at nearly every gas station or parking lot.

The downside was that the race-only exhaust was just a bit too loud. We couldn't use the car as aggressively as we intended, and it often sounded like we were driving with reckless abandon when all we were doing was pulling away modestly. That's called having your cake, and not getting to eat it. Meanwhile, we also acquired our next project car, a '68 Nova with a warmed-over 350 and a dual Flowmaster exhaust. It's been far too long since we spent time with a Flowmaster exhaust, and we had forgotten how much we liked them. While the Nova isn't what you'd call whisper quiet, it still allows cabin conversation, while providing the aggressive tone we like. We quickly arrived at the conclusion that this is how we wanted the Laguna to sound.

We thought this solution would let us have a lot more fun with the Laguna, so we ordered a pair of Flowmaster Super 44 Series mufflers. We know from prior dyno experience that X-pipes really do work, so we also ordered one of Flowmaster's universal 3-inch scavenging X-pipes. Surprisingly, our parts total only hit $360. The Flowmaster Super 44 Series is one of Flowmaster's newest mufflers, and was designed to provide the deep sound characteristic and flow capability of its 5-inch-case 50 Series muffler in a more compact 4-inch case for ground clearance. The result of over two years of development through dyno and track testing, the 44 Series makes use of Flowmaster's Delta Flow technology, and is made in Flowmaster's highly automated California assembly plant.

2/13

To help us with the system's minimal amount of fabrication and welding, we went down to The Muffler Man in Placentia, California, and proprietor Josh Gledhill had us out the door in about two hours (at about $150 in labor). We decided to go with axle turndowns instead of going over the axle-which saved us some labor, and allowed for any future suspension or frame modifications. (We also liked the sound of the turndowns on the Nova, so we went with that.)

3/13Our Laguna's new Flowmaster system would consist of a pair of 3-inch Super 44 mufflers and a 3-inch universal scavenging X-pipe. The X-pipe kit has a centersection, two header tubes, and two muffler tubes-these have slip-fit junctions where they meet the X-pipe. We also picked up two 3-inch header flanges. Total cost was $359.85, not including $150 labor to weld it together.

When we fired it up for the first time, we knew we made the right choice. There was plenty of boom and bravado, but without the sharp raspiness and razor-edged staccato of the open headers. We made a few sound level measurements with a Radio Shack sound level meter both before and after the exhaust swap, and discovered that the actual sound level was generally the same, but with some important differences. Outside the car, the old side-exit open-header design was louder at cruise rpm (2,000 and 2,500 rpm), just as we suspected. With the Flowmasters and the turndowns, we got lower exterior sound levels at the 2,000 and 2,500 rpm test points, but strangely, higher sound levels in the cockpit. The frequencies were lower, however, and not so much in the speech range. This actually makes conversation much easier, while still setting off the same number of car alarms in the parking lot! This brings up an interesting point: The perceived loudness has less to do with the actual sound level, and more to do with the frequencies in question. The proof is in the reduced driving fatigue, and the fact that we've had no problems with the cops since.

The science behind the Flowmaster Delta Flow technology is simple and effective. Traditional mufflers break down exhaust energy through entropic processes that convert the coherent movement of exhaust into increasingly smaller zones of turbulence, then eventually into heat energy. Mufflers with fiberglass packs and perforated surfaces all fall into that category. These do a great job of killing noise, but they don't use the exhaust energy to harness more power from the engine through pressure-wave tuning. Flowmaster pulls a big trick from the science of acoustical engineering by turning parts of the muffler into a Helmholtz resonator. By selecting key frequencies, and using those wavelengths to design the internal dimensions of cavities in the muffler, Flowmaster can cancel out specific frequencies (reference the chambers "A" and "E" in the cutaway diagram) without killing power. We call these annoying frequencies "donut" frequencies, because they tend to attract cops. Fewer donut frequencies mean fewer traffic stops, and we're all for that.

4/13We're lucky to have one of the best muffler shops around-The Muffler Man-just down the road from our Placentia office. Here, Gledhill positions the X-pipe at the centerline of the Laguna. He's already shortened one of the header pipes to place the X-pipe at the centerline.

Now we can finally enjoy the Laguna the way it was meant, and without undue interference from law enforcement. Next month we show you how the experts at Just Dashes restored our dashboard.